What, exactly, are you claiming about this that was “illegal”? When you singup for Facebook, you agree that anything you post might be shared with others on the platform.
The Facebook developer platform became so limited in 2014 that most developers (including me) left. There was no point in developing apps for the social graph that had no ability to be use the social graph. But even prior to that, the sharing of this information with apps, even those authorized by a friend, wasn’t “illegal”. You agreed to it when you signed up for Facebook and voluntarily handed them your information. Even the idea that developers were supposed to delete the information they had before was just a civil agreement between the company and themselves - it wasn't illegal. Facebook can certainly sue them over it, but there are no violations of the law occurring here.
So what about this whole situation is "illegal"?